Static mesh collisions and lods in blender

I like make a static mesh model with custom collision and lods.
How add in the urho3d/blender a custom collision mesh in the mesh(no shapes, a hand made collision) :question:
I used the mesh creator of Urho3D to join multiple models for create 1 with lods, but how create the lods in the blender file ?

Help ? :unamused: